The XPS spectra of the metathesis catalyst tungsten oxide on silica gel

XPS spectra of supported and unsupported tungsten oxides before and after use in the metathesis reaction of propene are reported. It is shown that the broad peaks, usually measured for supported materials, are due to line broadening caused by differential charging. A new sample preparation technique is described which leads to a considerable reduction of the line broadening. Both XPS and X-ray diffraction show that in fresh catalysts a well-defined phase Of WO₃ is present. The reduction of the supported trioxide by propene to W₂₀O₅₈, as concluded from X-ray diffraction measurements, results in the formation of W^v - and/or W^IV -species in used catalysts. For unsupported WO₃ these lower valencies have been observed in the valence-band spectra.